Overvoltage can be caused by:

  • lightning striking a house, a power line or an area nearby;
  • the switching on or off of power lines or substations.

Overvoltage causes most damage to the power units of electrical appliances such as televisions, set top boxes or computers. A damaged power unit can sometimes also damage the appliance connected to it. Areas with regular thunderstorms or with a lot of overhead lines are at greater risk of overvoltage. Although our electricity system has surge protection devices installed, they do not always protect against lightning strikes. Lightning creates an electrical field that is very powerful and can cause overvoltage in power lines even if it does not strike the line directly.

For protection from overvoltage we recommend:

  • type 3 surge protection devices, which need to be installed directly before the appliance, or sockets with pre-installed protectors for extra sensitive electronic appliances no matter where your place of consumption is.
  • type 1 and type 2 surge protection devices or a type 1+2 combined protection device in the junction boxes of houses, especially houses in the riskier areas.

Voltage dips and fluctuations

Voltage dips and fluctuations can be caused by:

  • the switching on or off of power lines or substations;
  • breakdowns in power lines caused by trees falling on the lines, icing or similar events;
  • the start-up of powerful electric motors.

Voltage dips and fluctuations can particularly cause damage to sensitive electrical and electronic appliances and their power units. If lights are constantly flickering it can minimise the service life of the bulbs and make it harder to see clearly. Voltage dips and fluctuations are more common in urban and rural buildings near large industrial and production plants and factories.

For protection we recommend using:

  • voltage stabilisers;
  • a UPS.

Planned outages and breakdowns

Occasionally disruptions in the power lines are caused by breakdowns or are planned.

Breakdowns mainly occur because of:

  • short circuits or breakdowns in power lines, which may for example be caused by trees falling on a line;
  • damage caused to underground or overhead lines during construction work, usually in towns;
  • breakdowns in old power lines or substations.

Planned outages are necessary when we repair and maintain old electricity networks and build new ones. We notify customers about these outages in plenty of time.

Breakdowns or unexpected outages can last for a short or long time. Short outages of up to three minutes affect electronic appliances the most. Short outages mostly occur in towns, where it is possible to restore the electrical supply after a breakdown by using another line. Longer outages of more than three minutes occur in country areas where the electricity network mainly uses overhead lines.

Severe weather conditions such as heavy snowfall, trees falling in storms, icing on the wires or very low or high temperatures can affect the reliability of overhead lines and cause breakdowns. Breakdowns can also be caused by forestry or digging work in nearby areas.

If a breakdown occurs while you are working on your computer it might not save the files your were working on at that time. Switching caused by outages might also damage sensitive electrical appliances such as electronic clocks or set top boxes.

Sometimes the outage may not be complete, meaning that only one or two phases lose voltage. In this case most of your home appliances might work normally but you might not be able to start appliances that use three-phase electric motors such as chainsaws and electric pumps. In the worst case scenario they might even get broken.

For protection we recommend:

  • a UPS installed directly before the appliance for extra sensitive electronic appliances;
  • a generator during long-term electricity outages if you use electrical appliances that require a constant supply of electricity;
  • a special motor protection switch for appliances that work with 3-phase electric motors such as chainsaws.

You can find out more from electrical or construction shops.

We recommend that you unplug your electrical appliances when you leave home or when there is a thunderstorm.